Network centric warfare requires far reaching, highly reliable communication channels between assets for effective and efficient operation. These assets, such as naval ships and aircraft, may be separated by significant distances, including being positioned BLoS. Current methods of achieving BLoS communication between two assets include the use of relays, such as airborne platforms (e.g., aircraft) located at suitable elevations or intermediate distances between the assets for achieving line-of-sight communication between each asset and the relay(s). However during tactical operations, including those under hostile conditions, such relay arrangements may prove impossible or impractical to implement. Moreover, currently employed communication relay hardware can be expensive and unreliable (e.g., it may not be sufficiently robust). Alternative solutions include the use of satellite relays. However, in addition to being costly and requiring a line-of-sight (LoS) to the satellite, existing satellite communication systems may exhibit high latency and congestion. Each of these relay-based techniques is also inherently vulnerable to physical attack and jamming tactics, making them unreliable for use in hostile environments.
Some systems and methods having been implemented utilizing natural phenomena to achieve BLoS communication between one or more assets. For example, methods such as HF (ionospheric) and Near-Vertical Incidence Skywave (NVIS) communications utilize ionization by solar radiation. However, these methods can be limited by the diurnal solar cycle. Moreover, these methods do not reliably provide both substantial range and throughput, and can suffer from bandwidth congestion.
One potentially advantageous communication technique is the use of troposcatter and/or atmospheric ducting signal propagation to accomplish BLoS communications. For example, propagation losses for a duct-confined signal propagation path are linearly proportional to the range, compared to at least a range-squared loss for LoS propagation. Moreover, losses in the ducting due to aerosols are more than compensated for by the lower propagation loss due to the smaller spreading volume of the duct versus the isotropic case. For specific conditions, the use of ducting can provide an approximately 40 dB increase in signal strength at 1000 km for signals in the GHz range. However, the ducting layer also creates multiple signal pathways. Because the duct acts as a leaky waveguide the signal is reflected or absorbed into, for example, the sea surface (the bottom of the duct for a marine boundary layer duct) and the ill-defined duct transitions. As a result, multiple iterations or copies of a signal may arrive at different phases, as the different iterations have traversed different path lengths. If the phases of these different iterations add destructively, the signal level relative to noise declines, making detection more difficult. Thus, these multiple pathways reduce the maximum range for a given data rate. Additionally, intersymbol interference (ISI) due to the arrival of separate signal copies at different times will tend to degrade the signal; one or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit. The ISI due to this delay spread limits the maximum data rate without signal distortion. Similar issues are present with troposcatter propagation. Further still, while these methods have the potential to offer improved throughput with suitable range, their effectiveness depends on ever-changing atmospheric conditions. Accordingly, these methods tend to be unpredictable and unreliable, at least as currently implemented via dish antennas generating single carrier transmissions in a fixed frequency band.
Improved systems and methods for providing reliable, long-range BLoS communications between assets are desired.